As shown in FIG. 10, in a three-axis acceleration sensor, a reference direction is determined in advance for each axis: an x-axis, a y-axis and a z-axis. Here, generally, a reflow process is employed when mounting the three-axis acceleration sensor to a circuit board; however, overheating occurring in this reflow step results in deviation (deviation of the 0 g level) in the reference directions.
Here, FIG. 11 shows amounts of deviation of the 0 g level occurring when the three axis acceleration sensor was mounted to the circuit board by the reflow process. Although FIG. 11 is an example, deviation of −97.2 to 54 mg (−5 to +3 degrees) occurred in the x-axis direction; deviation of −61.2 to 64.8 mg (±3.5 degrees) occurred in the y-axis direction; and deviation of −180 to 36 mg (−10 to +2 degrees) occurred in the z-axis direction. Furthermore, the 0 g level of the three-axis acceleration sensor may deviate with time, temperature change in an environment for actual use, etc.
Accordingly, in the three-axis acceleration sensor, processing (calibration processing) to correct (calibrate) this amount of deviation is performed after the reflow process when mounted to the circuit board. By performing this calibration processing, the reference direction of each axis, which has deviated due to causes such as the reflow process, is recovered (for example, see Patent Document 1).
Moreover, in such a calibration method, in general, correction is performed such that any two directions of the x-axis direction, the y-axis direction and the z-axis direction are at the 0 g level. It should be noted that, in a case in which accurate calibration is performed, as shown in FIG. 12, the body is placed so as to be oriented in one direction, and calibration is performed for a first axial direction (x-axis direction in FIG. 12(A)) and a second axial direction (y-axis direction in FIG. 12(A)); and thereafter, the body is placed so as to be oriented in another direction, and calibration is performed for the first axial direction (x-axis direction in FIG. 12(A)) and a third axial direction (z-axis direction in FIG. 12(A)), thereby correcting deviation of the reference directions in all three axes.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-93552